Filter bags for vacuum cleaners which have a tubular bag and which, in addition to a closed end region, have a folded base, a so called block base, are known in the state of the art. Normally, filter bags of this type are manufactured from a paper material which can be processed in normal tubular bag plants. In the case of filter bags of this type, a corresponding retaining plate is generally fitted on the block base and has an opening through which the air to be cleaned is guided. The object of the block base resides in stabilising the filter bag and in forming a three-dimensional bag. Furthermore, the block base facilitates fitting of the bag in the vacuum cleaner.
In recent times, new developments have become known with respect to vacuum cleaner bag materials, such as are described for example in WO 01/03802 A1. A special nonwoven material comprising a plurality of layers of filter material, which are independent of each other, is disclosed therein. These independent layers are combined to form a filter material with specific properties. In practice, it has now been shown that vacuum cleaner bags which are produced with a nonwoven material of this type are significantly superior relative to those previously known with respect to the performance of the vacuum cleaner, in particular with respect to the dust storage capacity.
It is problematic with filter bags which are produced from a previously described material however that it is difficult to form a block base because of the floppiness of the bag material during bending.
There has been no lack of attempts to produce a remedy by means of specific solutions. One possibility for forming a block base in the case of a vacuum cleaner bag which is produced from a nonwoven material as described previously is described in DE 103 48 375 A1. In the case of production method disclosed there, the process thereby takes place such that, after formation of the tube, the latter is sealed on one side with formation of an at least partially sealed region. As a result, as described previously, of the fact that the tube is welded together after being cut, the result is a connection of both internally situated layers of the tubular bag in the edge region. In a subsequent method step, in the case of the previously described method, stabilisation of the base is then achieved by introducing a die and folding over the narrow sides on the base and gluing thereof.
The production method and also the dust filter bags formed with the production method therefore always have a central weld seam which is formed in the edge region and in the case of which the two inner sides respectively are welded to each other.
It is however disadvantageous with the previously described filter bags that these do not always provide a satisfactory result with respect to the stability of the base for the high requirements in the vacuum cleaner and the required different shapes of filter bag. Furthermore, the method for the production of filter bags according to DE 103 48 375 A1 is very complex and cost-intensive. Furthermore, the seam which is vertical can make gluing or welding of the retaining plate on the base very difficult. Leaks can only be avoided with difficulty.